I have Comcast too (Internet, Cable & Phone). They have a terrible reputation on several fronts. However, I have noticed a marked improvement over the last year or so. You call for help because something's wrong, you get someone who is polite, intelligent and has the power to get your problem fixed.

I'd call them up and state your complaint. I believe they may have some tests they can run from their end to check your speed. It's also possible the weather has affected the connection from the street and you're constantly re-transmitting information because it's not received correctly because of a loose or wet connection thus making your overall experience slower.

I recently complained of poor service and they replaced some connections at the pole in the street and my internet has never been faster!